1. Field of the Invention
The present invention relates to a rotary electric machine, and more particularly, to a structure of a stator of a rotary electric machine.
2. Description of the Related Art
A stator of a rotary electric machine includes a stator core provided with slots, a coil mounted to the stator core, and an insulator, which is mounted in each slot, for insulating the coil from the stator core.
Further, examples of the stator core include a cylindrical member formed by stacking thin steel plates in an overlapping state, and in which a plurality of slots extending in a central axis direction are provided in a circumferential direction at predetermined pitches so as to be opened to an inner peripheral side of the stator core.
Moreover, there has been proposed a stator core in which, when the coil is mounted to the stator core, the stator core is developed into a linear shape so that a gap at the slot becomes larger than a wire width of a coil conductor, which enables mounting of a conductor having a large wire width. In such a stator core, after the coil is mounted, both ends of the linear stator core are brought into abutment to each other to form an annular shape, and both the ends are jointed to each other by welding or the like.
Note that, as for the shape of the coil, there has been proposed a coil having a structure in which, on an outer side of an axial end surface of the stator core, coil ends of a conductor wire for use in the coil are bent back to be wave-wound. Moreover, there has been proposed another structure in which, in order to efficiently use a space of the slots in the above-mentioned structure, two sets of coils are mounted for each predetermined number of slots so that a set of two conductor wires alternately occupy an inner layer side and an outer layer side in a slot depth direction, and thus the coils are distributed and wound into six phases (see, for example, Japanese Patent Application Laid-open No. 2001-211584).
However, the performance of the rotary electric machine is significantly affected by the number of turns of the coil, and hence when the number of turns is limited, a performance design appropriate for the intended use cannot be done.
For example, in a case where the rotary electric machine is used as an AC generator for an automobile, when a relationship between an output current of the generator and an rpm of an engine, which is proportional to an rpm of a rotor, is considered, in a generator having a larger number of turns of the coil, an output current at low speed becomes lower and an output current at high speed becomes higher as compared to a generator having a smaller number of turns of the coil.
That is, although there are various needs in view of the balance in output current between at low speed and at high speed, because the number of coils in a slot is specified and the number of turns of the coil is an integer, there has been a problem in that the above-mentioned needs cannot be satisfied in some cases.
In order to solve such a problem, there has been proposed a structure in which Δ-connection of coils of integer turns and Y-connection of coils of integer turns are combined. In this structure, of two sets of three-phase coils of integer turns, one set of the three-phase coil is Δ-connected, and another set of the three-phase coil is connected to wire-connection portions of the Δ-connection. Thus, the two sets of the three-phase coils are arranged at slot positions to be in a state of being shifted by π/6 electrical angle from each other.
According to this structure, even when the number of turns of the two sets of the three-phase coils is an integer, the number of turns in a wire-connection state of the Δ-connection and the Y-connection can be the number of turns between integers (non-integer turn number) (see, for example, Japanese Patent Application Laid-open No. 2002-247787).
Further, as another method to solve the problem, there has been proposed a structure in which, in a rotary electric machine including a stator including a multi-phase winding formed of a plurality of phase windings, one end of one of the phase windings is connected to a middle point other than both ends of another of the phase windings in a cyclic manner among the plurality of phase windings.
In this structure, in a part at which the phase windings are connected to each other (a part from the one end to the middle point of each phase winding), it may be considered that Δ-connection is made by a plurality of phase windings. Further, in a part other than the above-mentioned part of the phase windings (a part from the middle point to another end of each phase winding), it may be considered that a part of Y-connected phase windings is connected in series to each wire-connection portion of the Δ-connection.
According to this structure, the windings connected in Δ-connection are substantially equivalent to windings connected in Y-connection having the number of turns multiplied by 1/√3. Therefore, the number of turns of the multi-phase winding in conversion with that of Y-connection is equivalent to the number of turns of Y-connection portion added with the number of turns obtained by multiplying the number of turns of the Δ-connection portion by 1/√3. Therefore, by only changing a position of the middle point connected with two of the phase windings, a ratio of number of turns of the Y-connection portion to the Δ-connection portion can be changed at small intervals (see, for example, Japanese Patent Application Laid-open No. 2002-281706).
However, the conventional technologies have the following problems.
When the rotary electric machine described in Japanese Patent Application Laid-open No. 2002-247787 is used as an AC generator for an automobile, in order to change the number of turns of the stator winding, the number of conductors to be housed in the slot of the stator is required to be changed, and hence the number of turns can only be changed in the range of integers. Therefore, the output characteristics discretely vary in accordance with the change of the number of turns in the range of integers. Thus, the desired output characteristics may not be obtained, and there is a problem in that the degree of freedom in design of the output characteristics is low.
In contrast, it is conceivable to employ a method of substantially setting the number of turns of the stator winding to a value other than an integer by reducing the number of conductors to be housed in a part of the slots of the stator. However, in this case, in the slot at which the number of conductors to be housed is reduced, the conductor filling factor is reduced to increase the gap inside the slot. Therefore, the conductors may easily vibrate, which may easily cause short circuit between the wires or between the wire and an inner wall of the slot. Thus, there arises a new problem in that the reliability of the AC generator is deteriorated.
Further, in the case where the number of the conductors to be housed is reduced only in apart of slots of the stator, as compared to a case where the stator winding is equally wound with respect to all of the slots, the manufacturing facility becomes more complicated, and there also arises a problem of cost increase.
Further, the rotary electric machine of Japanese Patent Application Laid-open No. 2002-281706 requires two sets of three-phase coils. Further, the number of turns of each of the two sets of the three-phase coils is an integer. Therefore, there is a problem in that the non-integer turn number cannot be freely obtained in a wire-connection state of the Δ-connection and the Y-connection.
Moreover, in a case where the rotary electric machine of Japanese Patent Application Laid-open No. 2002-281706 is used as an AC generator for an automobile, when the stator winding is formed by jointing electric conductors bent into a U-shape, in addition to the above-mentioned problems, it becomes difficult to change the number of turns of the stator winding itself, and there is also a problem in that it is practically impossible to change the output characteristics.
That is, for example, it is possible to change the number of electric conductors housed in each slot of the stator, but in accordance therewith, the number of connecting portions and the number of bending times of the electric conductors change. Therefore, it is necessary to significantly change the manufacturing facility, which causes significant increase in cost due to the complicated manufacturing facility.